Glass capillary columns have become increasingly important for use in chromatography due to significant advantages over metal. Of particular analytical importance is the relative catalytic inertness of glass, especially for high temperature chromatography. It is known, however, that stationary phase coating procedures useful for metal capillaries seldom yield high efficiency glass capillary columns, or columns which are satisfactorily stable. To overcome these drawbacks, glass surface modifications and treatments have been extensively studied. Among these are surface roughening procedures which theoretically should yield greatly enhanced column efficiency and stationary phase film stability.
Among the closest of these prior art methods to the invention are those which use hydrogen fluoride reagent to attack the glass surface. In this respect, both gaseous and aqueous hydrogen fluoride have been used for surface roughening of glass capillary columns. Aqueous hydrogen fluoride, however, does not, as used in typical procedures, apply a matte-etch to borosilicate glass, and treatment of flint or soft glass capillaries by either gaseous or aqueous hydrogen fluoride is extremely difficult to control. These procedures, therefore, are not currently widespread in use.
A more commonly applied method is that which relies on the decomposition of ammonium bifluoride (or, e.g., a fluorinated ether) which is deposited in the capillary, the ends of the capillary sealed, and the capillary subsequently heated to 450.degree. C. to generate hydrogen fluoride gas. This procedure causes what is referred to as "silica whisker" formations on the inner surface of the glass. The major shortcomings of this method remain a lack of satisfactory uniformity, frequently in the form of too severe an etch for chromatography purposes. In addition, the high temperature reaction with hydrogen fluoride gas poses severe potential hazards and must be approached with extreme care. This latter procedure, for more details, is described in some depth by Onuska, J. of Chrom., 142 (1977), pp. 117-125.
Yet another surface roughening procedure for glass capillaries for chromatography uses 10-20% aqueous potassium difluoride reactant which is added to the capillary bore, followed by rinsing with water to dissolve the reaction product (K.sub.2 SiF.sub.6), thus producing an eroded or roughened surface texture. The resultant etch is often gradient in nature, however, and thus not satisfactorily uniform along the length of the column.